Share This

The planet's deep oceans at times may absorb enough heat to flatten the rate of global warming for periods of as long as a decade even in the midst of longer-term warming, according to a new analysis led by the National Center for Atmospheric Research (NCAR).

Related Articles

The study, based on computer simulations of global climate, points to ocean layers deeper than 1,000 feet (300 meters) as the main location of the "missing heat" during periods such as the past decade when global air temperatures showed little trend. The findings also suggest that several more intervals like this can be expected over the next century, even as the trend toward overall warming continues.

"We will see global warming go through hiatus periods in the future," says NCAR's Gerald Meehl, lead author of the study. "However, these periods would likely last only about a decade or so, and warming would then resume. This study illustrates one reason why global temperatures do not simply rise in a straight line."

The research, by scientists at NCAR and the Bureau of Meteorology in Australia, is published online in Nature Climate Change. Funding for the study came from the National Science Foundation, NCAR's sponsor, and the Department of Energy.

Where the missing heat goes

The 2000s were Earth's warmest decade in more than a century of weather records. However, the single-year mark for warmest global temperature, which had been set in 1998, remained unmatched until 2010.

Yet emissions of greenhouse gases continued to climb during the 2000s, and satellite measurements showed that the discrepancy between incoming sunshine and outgoing radiation from Earth actually increased. This implied that heat was building up somewhere on Earth, according to a 2010 study published in Science by NCAR researchers Kevin Trenberth and John Fasullo.

The two scientists, who are coauthors on the new study, suggested that the oceans might be storing some of the heat that would otherwise go toward other processes, such as warming the atmosphere or land, or melting more ice and snow. Observations from a global network of buoys showed some warming in the upper ocean, but not enough to account for the global build-up of heat. Although scientists suspected the deep oceans were playing a role, few measurements were available to confirm that hypothesis.

To track where the heat was going, Meehl and colleagues used a powerful software tool known as the Community Climate System Model, which was developed by scientists at NCAR and the Department of Energy with colleagues at other organizations. Using the model's ability to portray complex interactions between the atmosphere, land, oceans, and sea ice, they performed five simulations of global temperatures.

The simulations, which were based on projections of future greenhouse gas emissions from human activities, indicated that temperatures would rise by several degrees during this century. But each simulation also showed periods in which temperatures would stabilize for about a decade before climbing again. For example, one simulation showed the global average rising by about 2.5 degrees Fahrenheit (1.4 degrees Celsius) between 2000 and 2100, but with two decade-long hiatus periods during the century.

During these hiatus periods, simulations showed that extra energy entered the oceans, with deeper layers absorbing a disproportionate amount of heat due to changes in oceanic circulation. The vast area of ocean below about 1,000 feet (300 meters) warmed by 18% to 19% more during hiatus periods than at other times. In contrast, the shallower global ocean above 1,000 feet warmed by 60% less than during non-hiatus periods in the simulation.

"This study suggests the missing energy has indeed been buried in the ocean," Trenberth says. "The heat has not disappeared, and so it cannot be ignored. It must have consequences."

A pattern like La Niña

The simulations also indicated that the oceanic warming during hiatus periods has a regional signature. During a hiatus, average sea-surface temperatures decrease across the tropical Pacific, while they tend to increase at higher latitudes, especially around 30°S and 30°N in the Pacific and between 35°N and 40°N in the Atlantic, where surface waters converge to push heat into deeper oceanic layers.

These patterns are similar to those observed during a La Niña event, according to Meehl. He adds that El Niño and La Niña events can be overlaid on top of a hiatus-related pattern. Global temperatures tend to drop slightly during La Niña, as cooler waters reach the surface of the tropical Pacific, and they rise slightly during El Niño, when those waters are warmer.

"The main hiatus in observed warming has corresponded with La Niña conditions, which is consistent with the simulations," Trenberth says.

The simulations were part of NCAR's contribution to the Coupled Model Intercomparison Project Phase 5 (CMIP5). They were run on supercomputers at NCAR's National Science Foundation-supported Climate Simulation Laboratory, and on supercomputers at Oak Ridge Leadership Computing Facility and the National Energy Research Scientific Computing Center, both supported by the Office of Science of the U.S. Department of Energy.

More From ScienceDaily

More Earth & Climate News

Featured Research

Mar. 3, 2015 — While studying a ground-nesting bird population near El Reno, Okla., a research team found that stress during a severe weather outbreak of May 31, 2013, had manifested itself into malformations in ... full story

Mar. 3, 2015 — Researchers studied quartz from the San Andreas Fault at the microscopic scale, the scale at which earthquake-triggering stresses originate. The results could one day lead to a better understanding ... full story

Mar. 3, 2015 — The 3-D printing scene, a growing favorite of do-it-yourselfers, has spread to the study of plasma physics. With a series of experiments, researchers have found that 3-D printers can be an important ... full story

Mar. 3, 2015 — Researchers have developed a new way of rapidly screening yeasts that could help produce more sustainable biofuels. The new technique could also be a boon in the search for new ways of deriving ... full story

Mar. 3, 2015 — For almost a century, scientists have been puzzled by a process that is crucial to much of the life in Earth's oceans: Why does calcium carbonate, the tough material of seashells and corals, ... full story

Mar. 3, 2015 — Major cities in the UK are falling behind their international counterparts in terms of their use of smart technologies, according to a new study. The research has found that smart cities in the UK, ... full story

Mar. 3, 2015 — To simulate chimp behavior, scientists created a computer model based on equations normally used to describe the movement of atoms and molecules in a confined space. An interdisciplinary research ... full story

Mar. 3, 2015 — Rather than just waiting patiently for any pollinator that comes their way to start the next generation of seeds, some plants appear to recognize the best suitors and 'turn on' to increase the chance ... full story

Mar. 3, 2015 — Methane emissions are strongly reduced in lakes with anoxic bottom waters. But – contrary to what has previously been assumed – methane removal is not always due to archaea or anaerobic bacteria. ... full story

Featured Videos

Looted and Leaking, South Sudan's Oil Wells Pose Health Risk

AFP (Mar. 3, 2015) — Thick black puddles and a looted, leaking ruin are all that remain of the Thar Jath oil treatment facility, once a crucial part of South Sudan&apos;s mainstay industry. Duration: 01:13
Video provided by AFP

Related Stories

Oct. 6, 2014 — Using satellite observations and a large suite of climate models, scientists have found that long-term ocean warming in the upper 700 meters of Southern Hemisphere oceans has likely been ... full story

Sep. 11, 2014 — A hiatus in global warming ongoing since 2001 is due to a combination of a natural cooling phase, known as multidecadal variability (MDV) and a downturn of the secular warming trend. The exact causes ... full story

Feb. 9, 2014 — Heat stored in the western Pacific Ocean caused by an unprecedented strengthening of the equatorial trade winds appears to be largely responsible for the hiatus in surface warming observed over the ... full story

Nov. 13, 2013 — Scientists say they have found "missing heat" in Earth's climate system, casting doubt on suggestions that global warming has slowed or stopped over the past decade. The new research ... full story

May 28, 2013 — A new NASA and university analysis of ocean data collected more than 135 years ago by the crew of the HMS Challenger oceanographic expedition provides further confirmation that human activities have ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.